Method for coupling a pair of cylindrical members in end-to-end abutment



Jan. 7, 1964 A. B. NEPPLE 3,116,547

METHOD FOR COUPLING A PAIR OF CYLINDRICAL MEMBERS IN END-TO-END ABUTMENTOriginal Filed March 8, 1960 \ummuuuuununuumu FIG 3.

ARTHUR B. NEPPLE INVENTOR.

BY I

ATTORNEY United States Patent Office 3,116,547 METHGD FOR CDUPLTNG APAIR OF CYLINDRI- CAL MEMBERS IN END-TO-END ABU'I'NIENT Arthur B.Nepple, Rocltville, Md, assignor to the United fitat-es of America asrepresented by the Secretary of the Navy Original application Mar. 8,1960, Ser. No. 13,663, new Patent No. 3,103,887, dated Sept. 17, 1963.Divided and this application Mar. 2, 1962, Ser. No. 184,622 2 Claims.(Cl. 29-460) The present invention relates to an attaching and couplingmeans and more particularly to a method of securing a relatively thinshelled member to a second member. This application is a division ofcopending U.S. patent application Serial No. 13,663, filed March 8,1960, now Patent Number 3,103,887, by the same inventor.

Attaching problems arise whenever relatively thin walled members are tobe joined to another member, especially when the first member is ofbrittle material and the structural loads encountered are ofconsiderable magnitude. Such conditions are present in certain missiledesigns where ceramic material is used in airframe primary structuresbecause of the favorable characteristics of such materials in a hightemperature environment. It is apparent that this use of ceramicmaterial will create a special requirement for satisfactoryceramic-to-metal and ceramic-to-ceramic attachments. Because of therelatively low tensile strength of ceramics as compared to steel, andbecause of its complete lack of ductility, it is not feasible to utilizeconventional attaching methods. The attachment must not only withstandthe structural loads over wide temperature ranges, but also must performsatisfactorily through high heating rates, since under these conditions,the thermal stresses resulting from differential expansion andtemperature gradients will add to the ordinary structural loads. Thesatisfactory attachment must also maintain the assembly in coupledrelationship with a high degree of stiffness. In missiles having a highfineness ratio, that is, a high length to diameter ratio, it isextremely desirable to maintain overall stiffness in order that thenatural frequency of the missile structure be high. Structuraladvantages as well as opera tional advantages accrue from a high naturalfrequency in a missile structure. Other obvious requirements of asatisfactory attachment are low weight, small cross-section, fabricationcost and ease of assembly.

It is therefore the principal object of the present invention to providea suitable attachment method for coupling a thin-shelled brittle membersuch as a missile radome to a second member such as a missile body. Thepresent invention will not only provide a satisfactory coupling from astructural standpoint with high strength, low weight and cross-section,but will also provide advantageous features such as elimination ofcertain inherent electrical problems, avoidance of use of criticalmaterials, and ease and low cost of fabrication. While the presentinvention is herein described in connection with a ceramic radome and ametal missile body, it will readily be seen that it is applicable as anattachment device for ceramicto-ceramic or metal-to-metal connections.

Briefly, the present invention comprises a ring of glass fibers or otherhigh strength filament wrapped under tension and cured onto one of themembers to be joined in such manner as to produce a residual stress inthe ring. The resulting assembly of the ring and member is then securedto the other member by a plurality of mechanical fasteners. Presence ofthe residual stress in the ring provides a strong combinationbonded-mechanical joint which will withstand high stresses ofdifferential thermal expansions as well as of severe structural loads.In a ceramic radome and metallic missile body application, the ceramic3,116,547 Patented Jan. 7, 1964 radome is encircled by the glass fiberring to produce a combination bonded-mechanical joint, shear fastenersbeing provided to secure the ring to the missile body.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings in which:

FIG. 1 is an elevation showing the missile radome coupled to a missilebody by the present invention;

FIG. 2 is an enlarged fragmentary section showing the glass fiber ringwrapped onto the ceramic radome; and

FIG. 3 is an enlarged fragmentary section showing the attaching details.

Referring now to the drawing in detail, FIG. 1 shows a missile 1GPhaving a ceramic radome 12 coupled toa missile body 1 by an attachment16 constituting the present invention.

In FIG. 2 it can be seen that the radome 12 is provided on the outerperiphery thereof with a groove 18 near the aft end of the radome, theforward portion of the groove being somewhat deeper than the rearwardportion. Positioned at the aft end of the radome 12 is a circular band25 having an inwardly depending flange 22 which abuts the radome and iscemented thereto. Girdling the radome 12 and band 20 is a glass fiberring 24 that is wrapped under tension and cured thereon so as to providea residual compressive stress in the ceramic radome.

In FIG. 3 it can be seen that a plurality of apertures 26 are formedaround the periphery of the band 2t and extend through the ring 2 theapertures being countersunk on the inner face of the band. Pressed intothe apertures 2-6 are inserts 2% which accommodate screws 30 forengagement with a forwardly extending flange 32 on the missile body 14.interposed between the end of the flange 32 and the flange 22 is a seal34.

It is seen then that the glass fiber ring 24 is first bonded to theceramic radome 12 and then mechanically fastened to the missile body 14to securely attach the radome to the missile body. Because the ring 24is formed with glass fibers wrapped under tension, a residual hooptension stress is produced therein which is maintained after curing.This tension in the glass fiber ring coupled with the fact that thegroove 18 is formed with a reverse taper provides a combinationbonded-mechanical joint and solves the problem of differentialexpansions since any thermal stress induced will be opposed by theresidual stress in the ring. While this pro-stress in tension in thering, with accompanying compressive pre-stress in the radome, preventsthe ring from loosening from the radome due to any temperature rise ofthe joint under high speed flight conditions, excessive prestress isundesirable since it results in excessive stresses in the radome. Also,excessive pressures within the glass fiber ring could tend to forceresin out.

The incorporation of the band Ztl, which is preferably made of steel,tends to maintain a better sealing surface and also tends to hold theinternal tolerance on surface mating to the missile body. Moreimportant, however, is the fact that the band 25) also provides a highmodulus and strength to resist compression fastener loads, and to retaintension pro-stress in the aft portion of the glass fiber ring 24 toresist compression fastener loads.

The tension wrapping of the radome 12 is best done by mounting it andthe band 2% in juxtaposition on a mandrel, a cement being applied to theabutting surfaces of the end of the radome and the flange 22 of the bandThe surface of the radome and band to receive the glass fiber Wrappingis wetted with an adhesive such as Epon VIII. Glass fibers in the formof tape such as Type XPISO or X1 126 produced by the Minnesota Miningand Manufacturing Co., is then wrapped onto the radorne and band undertension of the order of 125300 pounds depending on the amount ofpie-stressing desired. After one layer of the tape is wound tangentiallyonto the radome and band, the mandrel is stopped and, with the tensionmaintained on the tape, a layer of glass fibers with the fibers runningaxially is placed over the first layer. Adherence of the axial fiberlayer to the first layer is obtained by heating and softening the resinwith a Warm air dryer. Alternate layers of trangentially wound tape andaxial fibers are then installed onto the radome and band until thedesired thickness is obtained. Four or five of these alternate layershave been found to produce excellent results; however, it has beendiscovered that superior results have been obtained by overwrapping,that is, by wrapping a considerable excess of glass fiber material ontothe radome and band, and then machining to the desired diameter. By thismethod, greater hoop loading stresses in the ring have been attained.

The last layer of tangential tape may be sealed just before releasingthe tension by applying heat from a soldering iron. After the wrappingis completed, the radome, band and glass fiber ring are cured in an ovenfor about six or seven hours at approximately 300 F. Machining of theexcess glass fiber material is best accomplished after the curing step,and as previously mentioned, residual stresses remain in the ring andradorne after curing and machining.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. it is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

1. The method of attaching a ceramic radome to a metallic missile body,comprising the steps of grinding a peripheral groove in the outer wallof the radome near the rear face thereof, positioning an annular bandin, abutment with the rear face of said radome, wrapping a ringcomprising alternate layers of tangential and axial glass fibers ontosaid radome at said groove and onto said band until an excess of glassfiber material has been built up, said tangential fibers being appliedunder a tension force, curing the resulting assembly of said glass fiberring, radorne and band, machining off the excess glass fiber materialfrom said ring, and attaching said glass fiber ring and band by screwfasteners to missile body.

2. A method for coupling a pair of cylindrical members in end-to-endabutment, comprising the steps of forming a peripheral groove in theouter Wall of one of said members .ear the abutting end thereof,positioning an annular band in juxtaposition with the abutting end ofsaid one member, Wrapping a ring comprising alt nate layers oftangential and axial glass fibers onto said one member at said grooveand onto said band until an excess of said glass fiber material has beenbuilt up, said tangential fibers being applied under a sufiicienttension force so as to produce a residual tension stress in said ring,curing the resulting assembly of said one member, band and glass fiberring, machining off the excess glass fiber material from said ring, andattaching said glass fiber ring and band to the other of said pair ofmembers by screw fasteners.

References Cited in the file of this patent UNITED STATES PATENTS

1. THE METHOD OF ATTACHING A CERAMIC RADOME TO A METALLIC MISSILE BODY,COMPRISING THE STEPS OF GRINDING A PERIPHERAL GROOVE IN THE OUTER WALLOF THE RADOME NEAR THE REAR FACE THEREOF, POSITIONING AN ANNULAR BAND INABUTMENT WITH THE REAR FACE OF SAID RADOME, WRAPPING A RING COMPRISINGALTERNATE LAYERS OF TANGENTIAL AND AXIAL GLASS FIBERS ONTO SAID RADOMEAT SAID GROOVE AND ONTO SAID BAND UNTIL AN EXCESS OF GLASS FIBERMATERIAL HAS BEEN BUILT UP, SAID TANGENTIAL FIBERS BEING APPLIED UNDER ATENSION FORCE, CURING THE RESULTING OF SAID GLASS FIBER RING, RADOME ANDBAND, MACHINING OFF THE EXCESS GLASS FIBER MATERIAL FROM SAID RING, ANDATTACHING SAID GLASS FIBER RING AND BAND BY SCREW FASTENERS TO SAIDMISSILE BODY.